1. Field of the Invention
This invention relates to the field of herbicidal compositions, and particularly to compositions having contact herbicidal activity and accentuated systemic herbicidal activity, and to methods of using such compositions to control vegetation.
2. Description of the Art
Both urea and sulfuric acid are widely used for a variety of purposes in numerous industries as fertilizers, soil adjuvants, chemical treating agents, chemical precursors and reactants. They are sometimes useful in combination, particularly in the agricultural industry, when the simultaneous addition of urea and sulfur to the soil is desired. Sulfuric acid is known to be phytotoxic, has been used as a postemergent, contact herbicide on a variety of plants, and is registered with the United States Environmental Protection Agency for the elimination of certain weed plants from plots of growing onions and garlic.
A variety of systemic herbicides are well known and are commercially available. Some of these such as Roundup.RTM., the isopropylamine salt of N-(phosphonomethyl) glycine, are relatively broad spectrum in that they are active toward a wide variety of vegetation. Others are relatively more selective in that they preferentially attack a relatively limited spectrum of plant species. For instance, some systemics such as 2,4-dichlorophenoxyacetic acid, known as 2,4-D, can be used to preferentially control broadleafs in the presence of grasses. Others such as 2,2-dichloropropionic acid, known as Dalapon and by other names, selectively control grasses in the presence of broadleafs. Other types of selectivity are also available.
Systemic herbicides are those that are assimilated by susceptible vegetation and are then translocated to parts of the plant other than those contacted, The systemic herbicides generally, if not always, depend on such translocation for their activity. For instance, when applied to plant foliage, a systemic herbicide will be assimilated during transpiration, or otherwise, and transported throughout the entire plant so that it eliminates the undesired vegetation, roots and all.
Some systemic herbicides are effective only when applied to established, transpiring vegetation and are known as postemergent herbicides. Others, that may or may not be active postemergent, are also effective preemergent herbicides. Preemergent herbicides are assimilated either by the plant seed prior to germination, and/or are stable in the soil environment and enter the cotyledon--the first leaf, leaf pair, or whorl of leaves developed by the seed plant embryo--and thereafter translocate to and destroy all parts of the germinating seed prior to or shortly after emergence. A variety of pre- and postemergent systemic herbicides are identified, and their chemical and herbicidal properties are disclosed in the Farm Chemicals Handbook published annually by Farm Chemicals Magazine, Meister Publishing Company, Willoughby, Ohio.
A number of investigators have studied the effects of combining systemic herbicides with certain contact herbicides (other than those described herein), and consistently have found that the systemic herbicide's activity is markedly reduced or is eliminated altogether when used in such combinations. Furthermore, all of the known systemic herbicides are complex organic compounds that are chemically unstable in the presence of relatively concentrated sulfuric acid. Therefore, they cannot be used in combinations in which the contact herbicidal activity or soil adjuvant properties of sulfuric acid might be desirable.
Other problems associated with presently available systemic herbicidal compositions include their ecotoxicity, persistence in the environment, high cost of application at effective dosage rates, the lack of effective immediate vegetation control such as that available with contact herbicides, limited effectiveness on some more resistant forms of vegetation, and others. Accordingly, a need exists for improved systemic herbicidal compositions and methods of vegetation control capable of minimizing or eliminating these problems.
It is, therefore, a primary object of this invention to provide improved herbicidal compositions, solid compositions convertible to herbicidal compositions, and methods for the use of such compositions.
Another object of this invention is the provision of systemic herbicidal compositions with increased activity of the contained systemic herbicides.
Another object of this invention is the provision of herbicidal compositions and methods of their use which significantly reduce the amount of systemic herbicide required to control undesired vegetation, and thereby reduce the amount of systemic herbicide introduced into the environment.
Another object of this invention is the provision of compositions which exhibit both significant contact and systemic herbicidal activity and/or methods of their use.
Another object is the provision of compositions and methods for controlling undesired vegetation and simultaneously applying nutrient nitrogen and sulfur to the soil.
Another object is the provision of compositions containing significant amounts of sulfuric acid and one or more systemic herbicides that are chemically stable in the composition.
Other objects, aspects, and advantages of this invention will be apparent to one skilled in the art in view of the following disclosure and the appended claims.